Add categories descriptions

Signed-off-by: gearnode <bryan@frimin.fr>

controls/core/infra/README.md

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+# Secure your infrastructure
+
+## Why does it matter?
+
+Your infrastructure holds your sensitive data and makes sure your service is
+available to your customers. Protecting it from unauthorized access or attacks
+is key to prevent any data leak or service outage.
+
+## How can I proceed?
+
+To secure your infrastructure, you will need to:
+
+1. Understand what your are protecting
+2. Regulate access
+3. Log changes
+4. Fix known vulnerabilities